(1) Field of the Invention
The present invention relates to an information distribution apparatus, and more particularly, to an information distribution apparatus for a CATV system which is provided with an information distributing section (BAS or Broadband Access Shelf), to which a plurality of set-top boxes (STBs) are connected, and a distribution control section (BTS or Broadband Tributary Shelf) situated between the information distributing section and a head-end section.
(2) Description of the Related Art
FIG. 8 is a diagram illustrating an example of a configuration of a conventional cable television (CATV) system. Specifically, a distribution control section (hereinafter referred to as “BTS”) 102 is connected via a bidirectional optical cable 131 to a head-end section 101 which provides a variety of programs, and an information distributing section (hereinafter referred to as “BAS”) 103 is connected to the BTS 102 via a bidirectional optical cable 132. The BAS 103 is provided with ports 121, . . . , 122 to which set-top boxes (hereinafter referred to as “STBs”) 104-106, . . . , 107-109 are connected via coaxial cables 121a, . . . , 122a. The ports 121, . . . , 122 include 64 ports in total, and three STBs are connected to each port and are assigned identification numbers #1 to #3, respectively. Television sets (TVs) 114-116, . . . , 117-119, for example, are connected to the STBs 104-106, . . . , 107-109, respectively.
In the above configuration, information is transmitted using ATM cells, and each of the STBs makes a request for distribution of a desired program to the BTS 102 via the BAS 103. The BTS 102 selects the requested programs from among various programs transmitted thereto from the head-end section 101, then sets communication paths to the BAS for the respective STBs, and transmits the programs to the BAS. The BAS distributes the programs to the respective STBs.
In the conventional system, however, if both the STB 104 and the STB 107, for example, request the BTS 102 to distribute information on the same channel x, the BTS 102 separately sets communication paths to the BAS 103 for distributing the information on the channel x to the STB 104 and the STB 107, respectively. Namely, the information on the same channel x is transmitted separately between the BTS 102 and the BAS 103.
Moreover, since programs that are distributed by request tend to be limited to particular popular programs, there is a possibility that such unnecessary multiple transmission frequently takes place in large numbers between the BTS 102 and the BAS 103.
To prevent the unnecessary transmission, an identical program may be transmitted from the BTS 102 to the BAS 103 via a single communication path, and in this case, it is necessary that the BTS 102 should notify the BAS 103 of destination STBs to which the program is to be distributed. Notifying destination STBs, however, leads to increase in the traffic between the BTS 102 and the BAS 103, and since popular programs are not necessarily limited to one in number, moreover, destination STBs need to be notified separately for respective popular programs, further increasing the traffic. Also, the BAS 103 is unable to initiate the distribution of a program unless and until the notification of destination STBs is completed, giving rise to a problem that the program distribution is delayed for a time period required for the notification.